1. Field of the Invention
The present invention relates generally to a punch press for punching sheet-like workpieces such as sheet metals and, more particularly, to a punch press having a C-shaped frame in which a plurality of pairs of upper and lower punching tools are provided.
2. Description of the Prior Art
Heretofore, punch presses having upper and lower punching tools for punching sheet-like workpieces such as sheet metals have mostly employed C-shaped frames in which an overhead beam is supported by a column above a base in a cantilever manner. The punch presses of the C-shaped frame are advantageous in that they can be assembled and manufactured at comparatively low cost and they are convenient to operate in many respects such as feeding and positioning workpieces to be punched.
The conventional punch presses of the C-shaped frame, however, have had several distinct disadvantages in spite of the advantages. The original disadvantage is that the C-shaped frame is inevitably subjected to deflections of the overhead beam under punching load during punching operations. Also, the deflections of the C-shaped frame will cause change in vertical alignment of the upper and lower punching tools and will result in poor punching accuracy and short life of the punching tools.
In the past, therefore, it has been the general practice of the industry to use massive proportions for the C-shaped frame to overcome the above disadvantages or at least minimize them within some limits. Of course, however, the massive proportions of the C-shaped frame will increase substantially the cost of the press and where deep throats are needed to increase the capacity of the press the massive proportions will take up a substantial amount of the floorspace for the press.